Brake Master cylinder revisited- swap for Land rover unit

You may recall how I had rebuilt the BMC in this car using a new Girling seal kit. All seemed fine for a while...



... and I've done this before and its been fine period, but in this case after about 6 months I did notice brake fluid starting to pool beneath the servo. It actually stripped the nice new paint from my servo underneath the BMC so clearly this is not right.

Mixture of rainwater and brake fluid puddling beneath servo.

I had hoped it was simply a poor seal around the cap coupled with overfull reservoir and parking uphill but sadly this turned out not to be the case and I have to face facts, the bore of my MC was probably too far gone for new seals to effect anything but a temporary fix.

Trouble is that my car has an early cylinder; a Girling unit and replacements for this are hard to come by and expensive. I could get my old cylinder re-sleeved in stainless steel but this is also likely to cost around the £180 mark! I do like originality so I will save the original for later repair, but for the time being I decided to fit a replacement. Several reports on the net speak of using a Land Rover Defender cylinder  (part no NRC8690) which is readily available and substantially cheaper at around £40 all in!! Reports vary as to whether its a direct replacement or not since some people have found the brake unions have different threads.  So I bought one of these  cylinders and set about fitting it.

Defender BMC as received...nice and clean!

I wanted to be sure I could fit this cylinder with minimum adjustment so I measured the depth of the piston at the rear using a straight edge; this will need to match up with forward projection of the servo pushrod.

Measuring depth of piston

The answer is 16 mm which is within 1 mm of the clearance I determined on the Girling cylinder (15.7mm). I think this amount of movement is easily accommodated in brake pedal travel so I didn't try to adjust the pushrod**.

I later found that I did need to adjust this rod, the difference needs to be taken up here not at the pedal. I loosened the BMC and could pull the unit off the 2 studs without disconnecting any brake lines. I could then reach in with a pair of snipe-nosed pliers to hold the rod whilst unscrewing the domed end nut with a 8mm spanner. If you hold the BMC back down on the studs and at the same time press the brake pedal gently you can feel when the clearance has been taken up to leave only a slight pedal movement before the BMC is affected. I found that I needed about one half turn. However, I cannot be sure that this is a consequence of using the landrover cylinder with its 0.3mm extra depth, or simply the long-dead hand of the LBPO who may have fiddled with this adjustment before.

However, I did pretty quickly find one glaring difference between the old and new m/cs: The ports on the land rover cylinder are different sizes, that at the front is obviously larger!

Unequal ports on Landrover BMC

In contrast those on the Girling BMC are the same size!

Equal unions on existing Girling BMC

Investigation showed that both Girling ports and the rear port on the landrover cylinder are M10x1, the front port  on the LRD cylinder is M12x1. I will clearly need a new brake union from the cylinder to G valve. Both vehicles use 3/16 pipe at this point.

In the past when I've made up new pipes I've used copper- easy to flare and fit although its accepted that these pipes can become work hardened and fail more easily. This was for a lighter car with a rather different performance spec. The Lotus has got steel or cupronickel pipes, both of which are more durable... but they are also rather harder and my current flaring tool just wont do. I bought a Franklin brake pipe flaring tool suitable for 3/16" steel/kunifer brake pipe and some new kunifer piping. One advantage of this tool is that it does let you flare pipes in position on the vehicle so maybe its a useful addition to the toolkit anyway? I would have liked to get a Draper tool but this was almost double the price. Well I made up the new pipe with little difficulty. The Franklin tool is easier to use than the nut-cracker anvil type. I added the terminals and flared each end before bending the new pipe to match the old.

Old pipe removed

Kunifer pipe is also quite simple to bend and I could do this easily by hand but I wanted to try and get a neater finish than my usual attempts, so I used a mini pipe bender to get the curves. Marking this shows that the internal radius of a 90 deg bend is 5cm from the inner edge of the tool steady- red mark as below.

Red mark acting as a reference for pipe alignment.

Radius of bend 5cms from reference above.

I was able to bend the pipe easily with the pipe bender and refine the fit by hand using the old M/C to G-valve pipe and tested the fit using the old cylinder although of course the M12 union won't screw in to this one.

New pipe run tested on existing m/c

I made up two short pipes to bench bleed the new m/c  as I've described before although it would be easier if I'd made the pipes shorter. They do make plastic kits for this but for some reason they are only really available in the US. By the time you've paid postage or paid an importer the price is silly!

bench-bleeding system- copper pipes with clear plastic hoses completing the reservoir return- this lets you see any bubbles

I removed the old m/c and plugged all open pipes with nipple covers. I could then clean the servo and prime it where leaking brake fluid has stripped the paint. I resprayed that black and fitted the new BMC leaving the bench bleed pipes in position to prevent leakage.

Cleaned and primed servo

Everything fitted easily- even the original cap (with low fluid warning float) screwed into the new cylinder so I should maintain warning light function.

New cylinder in position

... another view

I still need to bleed the brakes but I will do that when (if) it ever stops raining! ... It took app. 100 ml to flush through the air in the rear left wheel farthest from the BMC. Less in the fronts which had only a little if any to bleed. Result:  nice firm pedal! However the travel was  quite long. Eventually I corrected this by adjustment of the servo pushrod- see above)